A novel injectable boron doped-mesoporous nano bioactive glass loaded-alginate composite hydrogel as a pulpotomy filling biomaterial for dentin regeneration

Abstract

Background: Different materials have been used as wound dressings after vital pulp therapies. Some of them have limitations such as delayed setting, difficult administration, slight degree of cytotoxicity, crown discoloration and high cost. Therefore, to overcome these disadvantages, composite scaffolds have been used in regenerative dentistry. This study aims to construct and characterize the physicochemical behavior of a novel injectable alginate hydrogel loaded with different bioactive glass nanoparticles in various concentrations as a regenerative pulpotomy filling material.

Methods: Alginate hydrogels were prepared by dissolving alginate powder in alcoholic distilled water containing mesoporous bioactive glass nanoparticles (MBG NPs) or boron-doped MBG NPs (BMBG NPs) at 10 and 20 wt% concentrations. The mixture was stirred and incubated overnight in a water bath at 50 ⁰ C to ensure complete solubility. A sterile dual-syringe system was used to mix the alginate solution with 20 wt% calcium chloride solution, forming the hydrogel upon extrusion. Then, constructed hydrogel specimens from all groups were characterized by FTIR, SEM, water uptake percentage (WA%), bioactivity and ion release, and cytotoxicity. Statistical analysis was done using One-Way ANOVA test for comparisons between groups, followed by multiple pairwise comparisons using Bonferroni adjusted significance level (p < 0.05).

Results: Alginate/BMBG loaded groups exhibited remarkable increase in porosity and pore size diameter [IIB1 (168), IIB2 (183) (µm)]. Similarly, WA% increased (~ 800%) which was statistically significant (p < 0.05). Alginate/BMBG loaded groups exhibited the strongest bioactive capability displaying prominent clusters of hydroxyapatite precipitates on hydrogel surfaces. Ca/P ratio of precipitates in IIA2 and IIB1 (1.6) were like Ca/P ratio for stoichiometric pure hydroxyapatite (1.67). MTT assay data revealed that the cell viability % of human gingival fibroblast cells have declined with increasing the concentration of both powders and hydrogel extracts in all groups after 24 and 48 h but still higher than the accepted cell viability % of (˃70%).

Conclusions: The outstanding laboratory performance of the injectable alginate/BMBGNPs (20 wt%) composite hydrogel suggested it as promising candidate for pulpotomy filling material potentially enhancing dentin regeneration in clinical applications.

Keywords: Boron NPs; Dentin regeneration; Injectable scaffolds; Mesoporous bioactive glass nanoparticles; Regenerative pulpotomy; Sodium alginate hydrogels.

Fig. 1

Assembled dual- syringe system

Fig. 2

FTIR spectra of sodium alginate powder (a), crosslinked unloaded sodium alginate hydrogel (control) (b), mesoporous bioactive glass nanoparticles (MBG NPs) (powder) (c), boron doped-mesoporous bioactive glass nanoparticles (BMBG NPs) (powder) (d), crosslinked sodium alginate /MBG NPs loaded hydrogel (e), and crosslinked sodium alginate/BMBG NPs loaded hydrogel (f)

Fig. 3

SEM images (surface view) of freeze dried crosslinked unloaded sodium alginate hydrogel (A), and mesoporous bioactive glass nanoparticles (MBG NPs) loaded-alginate composite hydrogel (B) (original magnification X8000, X20000)

Fig. 4

SEM images of freeze-dried cross-linked unloaded sodium alginate hydrogel (Control) revealing the nano size pore configuration (A) (surface view, original magnification X5000), (B) (cross-sectional view, original magnification X250)

Fig. 5

SEM images revealing surface morphology and pore size diameter of freeze-dried crosslinked sodium alginate hydrogel loaded with different MBG NPs, in various concentrations (10 and 20 wt%) as: Subgroup IIA1 [alginate/MBG NPs loaded hydrogel (10 wt%)] (A and C); subgroup IIA2 [alginate/MBG NPs loaded hydrogel (20 wt%)] (B and D); subgroup IIB1 [alginate/BMBG NPs loaded hydrogel (10 wt%)] (E and G); subgroup IIB2 [alginate/BMBG NPs loaded hydrogel (20 wt%)] (F and H). A, B, E, F (cross-sectional view, original magnification X250); C, D, G, H (surface view, original magnification X5000)

Fig. 6

Water uptake (%) of all studied groups after incubation in distilled water at 37^oC until an equilibrium swelling state was reached (A), weight variation percentage (%) of all studied groups after soaking in SBF solution for different time intervals (B)

Fig. 7

FTIR spectra of surfaces of specimens Group I: unloaded alginate hydrogel (a), Group IIA1: alginate/MBG NPs loaded hydrogel (10wt. %) (b), Group IIA2: alginate/MBG NPs loaded hydrogel (20wt. %) (c), Group IIB1: alginate/BMBG NPs loaded hydrogel (10wt. %) (d), and Group IIB2: alginate/BMBG NPs loaded hydrogel (20wt. %) (e) after incubation in SBF solution for times 0, 1, 3, 7, 14 and 21 days

Fig. 8

SEM images (surface view) of freeze-dried specimens of crosslinked unloaded alginate hydrogel (control) and alginate composite hydrogel loaded with different types and concentrations of MBG NPs after immersion in SBF for times 1, 3, 7, 14 and 21 days, as unloaded sodium alginate hydrogel (Group I) (control) (a, k, p, u original magnification X8000 and f original magnification X10000); alginate/MBG NPs loaded hydrogel (10 wt%) (Subgroup IIA1) (g, l, q, v original magnification 8000 and b original magnification X9500); alginate/MBG NPs loaded hydrogel (20 wt%) (Subgroup IIA2) (c, h, m, r, w original magnification X8000); alginate/ BMBG NPs loaded hydrogel (10 wt%) (Subgroup IIB1) (d, i, n, s, x original magnification X8000); alginate/BMBG NPs loaded hydrogel (20 wt%) (Subgroup IIB2) (e, j, o, t, y original magnification X8000)

Fig. 9

Temporal ions released calcium (A), phosphorous (B), silicon (C), and boron (D) concentrations (ppm) in SBF after immersion of prepared hydrogel specimens of all study groups

Fig. 10

Effect of specimen powder extracts on the viability of gingival cells (A, B); effect of prepared specimen extracts on the gingival fibroblast cells (C, D). Cells were exposed to the tested specimens at different concentrations (mg/mL) for 24 and 48 h. The cell viability test was assessed by using MTT assay. All values represent the average values from 3 experiments and expressed as mean ± SEM